1. Technical Field
The present invention relates to an electric optical device such as, for example, a liquid crystal display, a manufacturing method thereof, and an electronic device including the electric optical device, for example, such as a liquid crystal projector.
2. Related Art
A liquid crystal display which is an example of electric optical devices may be used as a light modulation unit (that is, a light valve) of, for example, a projection type display device. Strong light is incident to the light valve from a light source, and, at this time, if a semiconductor layer forming a TFT (thin film transistor) in the light valve is irradiated with the light, this results in a light leakage current, which causes flickering or pixel unevenness to occur in a display image. In order to prevent this, a light blocking film may be provided in a laminated structure as a light blocking mechanism for blocking the incident light.
Here, the TFT may be formed in a self-aligning manner by implanting an impurity into the semiconductor layer using a gate electrode as a mask during the manufacturing thereof. For example, JP-A-2008-77030 discloses a technique in which, in such a TFT, the gate electrode is made of a conductive material having a light blocking property, and the gate electrode is provided to fill in a groove formed along the semiconductor layer, thereby blocking light coming in a tilted direction from entering the semiconductor layer. Also, JP-A-2007-142320 discloses a technique in which a first layer of the gate electrode functioning as a mask when the semiconductor layer is formed in a self-aligning manner, and a second layer which is formed to be wider than the first layer in order to prevent light from a light source from entering the semiconductor layer, are formed, and thereby the TFT can be formed in the self-aligning manner and the light blocking property of the TFT can be improved.
However, the TFTs disclosed in JP-A-2008-77030 and JP-A-2007-142320 require an annealing process for activating the impurities implanted into the semiconductor layer after forming the gate electrode functioning as a light blocking film, during the manufacturing process. The gate electrode is made of a light blocking material with a relatively high OD (optical density) value such as, for example, titanium nitride (TiN), tungsten silicide (WSi), but if these materials are exposed to high temperature due to the annealing process, the OD value is lowered, and the light blocking property is deteriorated. For this reason, the TFTs disclosed in JP-A-2008-77030 and JP-A-2007-142320 have technical problems in that, due to the manufacturing process and the structural characteristics, the light blocking property of the gate electrode functioning as a light blocking film is reduced due to the annealing process, and thus it is difficult to sufficiently decrease the light leakage current.